Create a new Movie Clip, draw a circle and center it by selecting it and pressing Ctrl + Alt + 2 then Ctrl + Alt + 5.

Now, using the line tool, draw two lines from the center to the circle. This will be one slice:

Select only the slice and press F8; make it a button and choose any name you want.

Inside this new button fill the slice with a color and copy the "Up" frame to the "Over" frame.
In the "Over" frame draw the slice to a new position, so it goes out from the circle when the mouse is over.